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Despite previous support for plyometric training, optimal dosing strategies remain unclear. Purpose: To investigate vertical and horizontal jump kinetic performance following a low-volume plyometric stimulus with progressively increased session jump volume. Methods: Sixteen academy rugby players (20.0 [2.0] y; 103.0 [17.6] kg; 184.3 [5.5] cm) volunteered for this study. Vertical and horizontal jump sessions were conducted 1 week apart and consisted of a 40-jump low-volume plyometric stimulus using 4 exercises, after which volume was progressively increased to 200 jumps, using countermovement jump (CMJ) for vertical sessions and horizontal broad jump (HBJ) for horizontal sessions. Jump performance was assessed via force-plate analysis at baseline (PRE-0), following the low-volume plyometric stimulus (P-40), and every subsequent 10 jumps until the end of the session (P-50, P-60, P-70,... P-200). Results: The low-volume stimulus was effective in potentiating HBJ (2% to 5%) but not CMJ (0% to −7%) performance (P <.001). The HBJ performance enhancements were maintained throughout the entire high-volume session, while CMJ realized small but significant decrements (−5% to −7%) in jump height P-50 to P-80 before recovering to presession values. Moreover, increases in eccentric impulse (5% to 24%; P <.001) in both sessions were associated with decreased or maintained concentric impulse, indicating a breakdown in performance-augmenting mechanisms and less effective power transfer concentrically after moderate volumes. Conclusion: Practitioners should consider kinetic differences between HBJ and CMJ with increasing volume to better inform and understand session dosing strategies. [ABSTRACT FROM AUTHOR]

Introduction Warfighters are issued hard body armor designed to defeat ballistic projectiles. The resulting backface deformation can injure different thoracoabdominal organs. Developed over decades ago, the behind armor blunt impact criterion of maximum 44 mm depth in clay continues to be used independent of armor type or impact location on the thoracoabdominal region covered by the armor. Because thoracoabdominal components have different energy absorption capabilities, their mode of failures and mechanical properties are different. These considerations underscore the lack of effectiveness of using the single standard to cover all thoracoabdominal components to represent the same level of injury risk. The objective of this pilot study is to conduct cardiac impact tests with a live animal model and analyze biomechanical injury candidate metrics for behind armor blunt trauma applications. Materials and Methods Live swine tests were conducted after obtaining approvals from the U.S. DoD. Trachea tubes. An intravenous line were introduced into the swine before administering anesthesia. Pressure transducers were inserted into lungs and aorta. An indenter simulating backface deformation profiles produced by body armor from military-relevant ballistics to human cadavers delivered impact to the heart region. The approved test protocol included 6-hour monitoring and necropsies. Indenter accelerometer signals were processed to compute the velocity and deflection, and their peak magnitudes were obtained. The deflection-time signal was normalized with respect to chest depth along the impact axis. The peak magnitude of the viscous criterion, kinetic energy, force, momentum and stiffness were obtained. Results Out of the 8 specimens, 2 were sham controls. The mean total body mass and soft tissue thickness at the impact site were 81.1 ± 4.1 kg and 3.8 ± 1.1 cm. The peak velocities ranged from 30 to 59 m/s, normalized deflections ranged from 15 to 21%, and energies ranged from 105 to 407 J. The range in momentum and stiffness were 7.0 to 13.9 kg-m/s and 22.3 to 79.9 N/m. The maximum forces and impulse data ranged from 2.9 to 11.7 kN and 1.9 to 5.8 N-s. The peak viscous criterion ranged from 2.0 to 5.3 m/s. One animal did not sustain any injuries, 2 had cardiac injuries, and others had lung and skeletal injuries. Conclusions The present study applied blunt impact loads to the live swine cardiac region and determined potential candidate injury metrics for characterization. The sample size of 6 swine produced injuries ranging from none to pure skeletal to pure organ trauma. The viscous criterion metric associated with the response of the animal demonstrated a differing pattern than other variables with increasing velocity. These findings demonstrate that our live animal experimental design can be effectively used with testing additional samples to develop behind armor blunt injury criteria for cardiac trauma in the form of risk curves. Injury criteria obtained for cardiac trauma can be used to enhance the effectiveness of the body armor, reduce morbidity and mortality, and improve warfighter readiness in combat operations. [ABSTRACT FROM AUTHOR]

This study aimed to systematically review training methods prescribed to develop lower-body power, determine their effectiveness for the development of lower-body mechanical power and their implementation in an annual training cycle amongst team-sport athletes. The absolute and relative outcome values of concentric mean power, peak power and mean propulsive power were extracted from 19 studies. Outcomes were assessed using baseline to post intervention percent change, effect sizes, and the level of evidence concerning the method's effectiveness. A thorough analysis of the literature indicated that, based on the high level of evidence, traditional (e.g., strength training alone) and combination training (e.g., complex and contrast) methods should be considered. Further, optimal load and velocity-based training can be implemented if coaches have access to the appropriate equipment to monitor movement velocity and mechanical power in every session. This is of particular importance in periods of the season where high volumes of technical-tactical training and congested fixture periods are present. Also, flywheel, eccentric overload and weightlifting methods have been shown to be effective although the level of evidence is low. Future research should expand on current training practices whilst adequately reporting actual training loads from sport-specific training and games alongside strength-power training protocols. [ABSTRACT FROM AUTHOR]

The influence of electric current pulses passing between parts during fretting wear of titanium alloys is examined. A description of the test bench and a description of the test methodology are given. [ABSTRACT FROM AUTHOR]

We explore the viability of modeling dynamic problems with a new formulation of an impulse‐based Level‐Set DEM (LS‐DEM). The new formulation is stable, fast, and energy conservative. However, it can be numerically stiff when the assembly has substantial mass differences between particles. We also demonstrate the feasibility of modeling deformable structures in a rigid body framework and propose several enhancements to improve the convergence of collision resolution, including a hybrid time integration scheme to separately handle at rest contacts and dynamic collisions. Finally, we extend the impulse‐based LS‐DEM to include arbitrarily shaped topographic surfaces and exploit its algorithmic advantages to demonstrate the feasibility of modeling realistic behavior of granular flows. The new formulation significantly improves the performance of dynamic simulations by allowing larger time steps, which is advantageous for observing the full development of physical phenomena such as rock avalanches, which we present as an illustrative example. [ABSTRACT FROM AUTHOR]

Introduction While the 44-mm clay penetration criterion was developed in the 1970s for soft body armor applications, and the researchers acknowledged the need to conduct additional tests, the same behind the armor blunt trauma displacement limit is used for both soft and hard body armor evaluations and design considerations. Because the human thoraco-abdominal contents are heterogeneous, have different skeletal coverage, and have different functional requirements, the same level of penetration limit does not imply the same level of protection. It is important to determine the regional responses of different thoraco-abdominal organs to better describe human tolerance and improve the current behind armor blunt trauma standard. The purpose of this study was to report on the methods, procedures, and data collected from swine. Materials and Methods Live swine tests were conducted after obtaining approvals from the local institution and the Army Care and Use Review Office of the U.S. Department of Defense. Trachea tubes and an intravenous line were introduced before administering anesthesia. Pressure transducers were inserted into the lungs and aorta. An indenter simulating the backface deformation profiles produced by body armor from military-relevant ballistics to human cadavers was used to deliver impact loading to the liver region. A triaxial accelerometer was included in the indenter design. The animals were monitored for 6 hours, necropsies were performed, and injuries were identified. Biomechanical data of the energy, velocity, deflection, viscous criterion, force, and impulse variables were obtained for each test. Results Peak accelerations, velocities, deflections, forces, impulse, and energies ranged from 897 to 5,808 g, 21 to 59 m/s, 1.96 to 8.87 cm, 2.3 to 13.1 kN, 1.1 to 7.1 Ns, and 58 to 387 J, respectively. The peak viscous criterion ranged from 0.8 to 5.8 m/s. All animals survived the 6-hour survival period. Three animals responded with liver lacerations while the remaining 4 did not have any injuries. Conclusion The experimental design based on parallel tests with whole body human cadavers and cadaver swine was found to be successful in delivering controlled impacts to the liver region of live swine and reproducing liver injuries. Previously used biomechanical measures as potential candidates for injury criteria development were obtained. Using this proven model, tests with additional samples are needed to develop injury risk curves for liver impacts and obtain regional (liver) injury criteria. [ABSTRACT FROM AUTHOR]

Practitioners consider the role of the legs in the game of tennis as fundamental to achieve high performance. But, the exact link between leg actions and high-speed and accurate serves still lacks understanding. Here, we investigate the correlation between force-time curve variables during serve leg drive and serve performance indicators. Thirty-six competitive players performed fast serves, on 2 force plates, to measure ground reaction forces (GRF). Correlation coefficients describe the relationships between maximal racket head velocity, impact height, and force-time curve variables. Among all the variables tested, the elapsed time between the instants of maximal vertical and maximal anteroposterior GRF (r = -0.519, p < 0.001) and the elapsed time between the instant of maximal ante-roposterior GRF and ball impact (r = -0.522, p < 0.001) are the best predictors of maximal racket velocity. Maximal racket head velocity did not significantly correlate with the mean or maximal vertical GRF or with the mean or maximum rate of vertical force development. The best predictor for impact height is the relative net vertical impulse during the concentric phase (r = 0.772, p < 0.001). This work contributes to a better understanding of the mechanical demands of tennis serve motion and gives guidelines to improve players preparation and performance. Trainers should encourage their players to better synchronize their upward and forward pushing action during the serve to increase maximal racket head velocity. Players should also aim to improve their relative net vertical impulse to increase impact height through strength training and technical instructions. [ABSTRACT FROM AUTHOR]

Sprint skating is essential for competitive success in hockey. Previous studies have highlighted various measures of lower-body strength and power as key factors influencing sprint performance. However, while these studies have indicated a significant association between the ability to exert greater force and impulse into the ice surface, and the capacity to achieve faster sprint skating speeds, the direct relationship between these factors remains largely inferred. What are the relationships between insole plantar force variables, sprint skating performance, and their association with physical capacity measures, in national-level male hockey athletes? Athletes (n=13) performed 25 m sprint skating trials with insole force sensors and completed: ankle dorsiflexion and hip abduction range-of-motion (ROM), countermovement jump (CMJ), seated single-leg jump, and 10–5 repeated-hop test (RHT) assessments. Relationships were assessed using Kendall's Tau rank correlations (τ), with significant relationships identified between mean relative weight acceptance impulse [WAI] and 0–5 m (τ=0.47) and total distance (τ=0.46) times. Additionally, significant associations were observed between mean relative WAI and: CMJ relative eccentric deceleration impulse (τ=0.44), CMJ eccentric peak velocity (τ=-0.46) and RHT concentric impulse (τ=-0.56). Finally, significant relationships were identified between mean relative PI for all strides and the 10–20 m split, with peak velocity (PV) (τ=-0.58 to −0.73); and between ankle dorsiflexion ROM and PV (τ=-0.57). Athletes with faster initial acceleration and overall sprint performance times demonstrated lower relative WAI during their strides and employed a jump strategy that optimized concentric impulse with a rapid eccentric phase. To attain a high PV the athletes appeared to require a stride that maximized glide and minimized vertical force, with greater ankle dorsiflexion ROM potentially facilitating this. • Insole force variables were significantly related to sprint skating performance. • Lower relative WAI was associated with faster 25 m time and initial acceleration. • Performance in the RHT and CMJ were associated with sprint performance. • Greater ankle dorsiflexion may facilitate a stride with more glide and less drag. [ABSTRACT FROM AUTHOR]

Introduction Cumulative low-level blast exposure during military training may be a significant occupational hazard, increasing the risk of poor long-term outcomes in brain function. US Public Law 116-92 section 717 mandates that US Department of Defense agencies document the blast exposure of each Service member to help inform later disability and health care decisions. However, which empirical measures of training blast exposure, such as the number of incidents, peak overpressure, or impulse, best inform changes in the neurobehavioral symptoms reflecting brain health have not been established. Materials and Methods This study was approved by the US Army Special Operations Command, the University of North Carolina at Chapel Hill, and the VA Puget Sound Health Care System. Using methods easily deployable across different organizational structures, this study sought to identify and measure candidate risk factors related to career occupational blast exposure predictive of changes in neurobehavioral symptom burden. Blast dosimetry-symptom relationships were first evaluated in mice and then tested in a military training environment. In mice, the righting time neurobehavioral response was measured after exposure to a repetitive low-level blast paradigm modeled after Special Operations training. In the military training environment, 23 trainees enrolled in a 6-week explosive breaching training course, 13 instructors, and 10 Service member controls without blast exposure participated in the study (46 total). All participants provided weekly Neurobehavioral Symptom Inventory (NSI) surveys. Peak blast overpressure, impulse, total number of blasts, Time in Low-Level Blast Occupation, and Time in Service were analyzed by Bayesian analysis of regression modeling to determine their probability of influence on the post-training symptoms reported by participants. Results We tested the hypothesis that cumulative measures of low-level blast exposure were predictive of changes in neurobehavioral symptoms. In mice, repetitive blast resulted in reduced righting times correlated with cumulative blast impulse. In Service members, peak blast overpressure, impulse, total number of blasts, Time in Low-Level Blast Occupation, and Time in Service all showed strong evidence of influence on NSI scores after blast exposure. However, only models including baseline NSI scores and cumulative blast impulse provided significant predictive value following validation. Conclusions These results indicate that measures of cumulative blast impulse may have utility in predicting changes in NSI scores. Such paired dosimetry-symptom measures are expected to be an important tool in safely guiding Service members' occupational exposure and optimizing force readiness and lethality. [ABSTRACT FROM AUTHOR]

This paper examines the intricate dynamics of the logistic map involving impulsive forces that depend on the state. The conditions of stability and border-collision bifurcation (BCB) of periodic orbits are presented. The two-parameter dynamical regions and the two-parameter bifurcation diagram of the system with respect to the system parameter and the strength of impulsive force are constructed. The periodic tongues are given to show that the BCB is critical for the dynamics of the logistic map with state-dependent impulsive forces. Finally, the bifurcation curves are provided to disclose the mechanisms of several bifurcation scenarios closely related to the BCB, including the period increment scenario and the period-adding scenario. [ABSTRACT FROM AUTHOR]

In this paper, we investigated the adaptive exponential synchronization problem of impulsive coupled neutral stochastic neural networks with Lévy noise and probabilistic delays under non-Lipschitz conditions. A stochastic variable with a Bernoulli distribution was utilized to transform the information regarding probabilistic delays into a model featuring deterministic time delays and stochastic parameters. In the context of adaptive controllers, exponential synchronization conditions depending on the delay, noise intensity, and impulse factor were derived using Lyapunov-Krasovskii functions, the nature of Lévy noise, and some inequality methods. To provide further support for the proposed approach, two numerical illustrations were presented. [ABSTRACT FROM AUTHOR]

The study of blast loads on structures is important due to the potential of significant consequences in various scenarios. From terrorist attacks to industrial accidents, comprehending how structures respond to blast waves is critical for ensuring public safety and designing resilient structures. Studying these effects typically involves two main methods: free-field tests with live explosives and shock tube tests. Although shock tube testing offers certain advantages, both approaches are costly and demand significant space. This research aims to develop a cost-effective and straightforward technique for generating stress waves that closely replicate the progressive and spatial characteristics of free-field or shock tube blast waves. This method was designed to evaluate the dynamic response of laminated glass panels. The stress wave was generated by impacting a piston on the fluid inside a tube, which was connected to a fluid chamber. This setup produced impulsive loads that were distributed across a laminated glass test panel. Moreover, it was used to simulate the shock near filed explosions for a certain part of a structure. High-speed cameras were utilized to analyze the initial velocity of flying glass fragments. The apparatus successfully produced various blast waves and impulsive profiles for different drop weight heights. The initial velocities of randomly selected flying shards ranged from 3 m/s to 4 m/s. [ABSTRACT FROM AUTHOR]

The study of blast loads on structures is important due to the potential of significant consequences in various scenarios. From terrorist attacks to industrial accidents, comprehending how structures respond to blast waves is critical for ensuring public safety and designing resilient structures. Studying these effects typically involves two main methods: free-field tests with live explosives and shock tube tests. Although shock tube testing offers certain advantages, both approaches are costly and demand significant space. This research aims to develop a cost-effective and straightforward technique for generating stress waves that closely replicate the progressive and spatial characteristics of free-field or shock tube blast waves. This method was designed to evaluate the dynamic response of laminated glass panels. The stress wave was generated by impacting a piston on the fluid inside a tube, which was connected to a fluid chamber. This setup produced impulsive loads that were distributed across a laminated glass test panel. Moreover, it was used to simulate the shock near filed explosions for a certain part of a structure. High-speed cameras were utilized to analyze the initial velocity of flying glass fragments. The apparatus successfully produced various blast waves and impulsive profiles for different drop weight heights. The initial velocities of randomly selected flying shards ranged from 3 m/s to 4 m/s.

Step‐up variations are frequently used in sports performance to develop coordinated and powerful movements that transfer to running. This study aimed to quantify the kinetic characteristics of the first foot contact of four different step‐up variations. Ten professional rugby league players participated in this study and performed the Barbell One Box Step‐Up with Catch (BB1), Barbell Two Box Step‐Up (BB2), Vest Two Box Run (VEST) and Step‐Up Jump (JUMP) as part of routine in‐season strength training sessions during one season. Peak force, total impulse and maximal rate of force development (RFD) were measured from first foot contact on the step‐up box. Significantly greater peak force and RFD were observed in JUMP than any other variation (standardized mean difference; SMD: 3.9–5.5; p < 0.001). Total impulse was equal between JUMP and BB1, and significantly greater in JUMP than BB2 and VEST (SMD: 1.3–2.3; p < 0.001), and in BB1 than BB2 and VEST (SMD: 1.8–2.8; p < 0.001). Significantly larger peak force and RFD were observed in BB2 and VEST than BB1 (SMD: 0.6–0.7) and in total impulse in BB2 than VEST (SMD: 1.6) (p < 0.05). The results of this study highlight that step‐up exercise variations maximize different kinetic characteristics, which may transfer differently to athlete running performance. Highlights: The Step‐Up Jump variation was shown to produce the largest relative peak force, largest rate of force development (RFD) and equal largest total impulse and therefore may have the greatest transferability to maximal speed running through the maximization of the stance phase.The Barbell Two Box Step‐Up (BB2) and Vest Two Box Run (VEST), produced significantly greater peak relative force and RFD than the Barbell One Box Step‐Up with Catch (BB1) and therefore may have better transferability to acceleration ability.Coaches can use the findings of this study to assist their selection of step‐up variations that are best suited to develop running ability and should consider the testing results and individual requirements of each athlete. [ABSTRACT FROM AUTHOR]

This paper studies global exponential stability (GES) of discrete-time (D-T) BAM neural networks (BAMNNs) affected by impulses and time-varying delays. An impulse-free D-T BAMNN with time-varying delays is first developed via the properties of M-matrices, and then the relation between the solutions of the original and new BAMNNs is established. From which, sufficient conditions for GES of the original BAMNN are derived by investigating GES conditions of the new BAMNN based on the counter-evidence and the nature of the nonsingular M-matrix. The results of illustrative examples show that the obtained GES criteria are effective. By comparing with previous results, this paper has the following three merits: (a) the obtained GES criteria are to check the positivity of eigenvalues of a constant matrix, which is easy to realize; (b) this method can be used for other D-T system models affected by impulses and time-varying delays; and (c) the numerical results show that our method is less conservative than ones in other literatures. [ABSTRACT FROM AUTHOR]

The aim of this study was to explore the kinetics and kinematics across incremental loads with the push press (PP), push jerk (PJ), and split jerk (SJ). Eighteen resistance-trained men performed the 1 repetition maximum (1RM) tests (visit 1)3-7 days before an incremental loading protocol (60, 75, and 90% 1RM) of the 3 exercises (visit 2). Kinetics and kinematics were derived from force-time data and compared using a repeated-measures analysis of variance with load and exercise as within-subject factors. Dependent variables for the biomechanics assessment were categorized as output (power and impulse), driver (force and work), and strategy (displacement and duration) metrics. The interrepetition reliability was assessed using the intraclass correlation coefficient and coefficient of variation. The PP, PJ, and SJ 1RM performance were 89.7 ± 15.4, 95.6 ± 14.4, and 103.0 ± 16.9 kg, respectively. Driver, strategy, and outcome metrics displayed moderate-to-excellent (intraclass correlation coefficient: 0.58-0.98) reliability with acceptable variability (% co-efficient of variation: 2.02-10.00). Increased load resulted in significantly large increases in force, work, displacement, duration, power, and impulse (p < 0.001, ηp² = 0.534-0.903). Exercise selection had a significant and large effect on power, impulse, work, and force (p < 0.016, ηp² = 0.387-0.534). There was a significant and large effect of load x exercise interaction on work, displacement, and duration (p < 0.019, ηp² = 0.158-0.220). Practitioners are encouraged to use heavier loads (90 > 75 > 60% 1RM) during the SJ exercise to maximize output, driver, and strategy kinetics and kinematics. [ABSTRACT FROM AUTHOR]

In this paper, we present a method to achieve exponential stability in a class of impulsive delayed neural networks containing parameter uncertainties, time-varying delays, and impulsive effect and reaction–diffusion terms. By using an integro-differential inequality with impulsive initial conditions and employing the M-matrix theory and the nonlinear measure approach, some new sufficient conditions ensuring the global exponential stability and global robust exponential stability of the considered system are derived. In particular, the results obtained are presented by simple algebraic inequalities, which are certainly more concise than the previous methods. By comparisons and examples, it is shown that the results obtained are effective and useful. [ABSTRACT FROM AUTHOR]

Flatfoot (pes planus) is a common foot deformity, and its causes are mainly related to age, gender, weight, and genetics. Previous studies have shown that custom-made insoles could have a positive effect in improving plantar pressure and symptoms in individuals with flexible flatfeet, but it remains to be explored whether they can still show benefits in daily walking on different slopes. This study aims to investigate a custom-made insole based on plantar pressure redistribution and to verify its effectiveness by gait analysis on different slopes. We recruited 10 subjects and compared the peak pressure and impulse in each area between custom-made insole (CI) and ordinary insole (OI) groups. The results illustrate that CI raises the pressure in T area, improves the ability of the subjects to move forward in the slope walking, which was beneficial to gait stability. The redistribution of pressure in MF and MH area is promoted to provide active protection for subjects. Meanwhile, CI could decrease the impulse in MF area during uphill and level walking, which effectively reduces the accumulation of fatigue during gait. Moreover, avoiding downhill walking could be able to protect foot from injury in daily life. [ABSTRACT FROM AUTHOR]

Flatfoot is a structural and functional deformity of the foot that might change ground reaction force variables of gait. Evaluating the components of ground reaction force in three dimensions during gait is considered clinically important. This study aimed to investigate the components of ground reaction force, impulse, and loading rate during gait in people with flexible and rigid flatfoot compared to healthy subjects. 20 young women with flatfoot in two experimental groups (10 with rigid flatfoot and 10 with flexible flatfoot) and 10 healthy women in the control group participated in this study. Ground reaction force components during gait were measured using two force plates. The peak of ground reaction forces, impulse, and loading rate were then extracted. Data were processed and analyzed using MATLAB and SPSS software. One-way ANOVA with a significant level (P˂0.05) was used for statistical analysis. The results showed that peak braking force was higher in the rigid flatfoot group than in the control group (p = 0.016) and the flexible flatfoot group (p = 0.003). The posterior force loading rate was significantly higher in the rigid flatfoot group than in the flexible flatfoot group (P = 0.04). There was no significant difference in vertical loading rate between groups (P˃0.05). Since the maximal posterior ground reaction force was higher in the subjects with rigid flatfoot than in those with flexible flatfoot and healthy subjects, the increase in posterior ground reaction force is associated with an increase in anterior shear force at the knee. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Jilin University (Science Edition) / Jilin Daxue Xuebao (Lixue Ban) is the property of Zhongguo Xue shu qi Kan (Guang Pan Ban) Dian zi Za zhi She and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Zhejiang University (Science Edition) is the property of Journal of Zhejiang University (Science Edition) Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

BACKGROUND: Human plantar pressure can reflect the health status of the lower limbs and even the whole body, which is an important basis for gait analysis, and body mass index is an important influencing factor. OBJECTIVE: To investigate the effect of body mass index on plantar pressure. METHODS: Twenty young college students from Xuzhou Medical University, including 10 males and 10 females aged 19-21 years, were selected as test subjects and divided into three groups according to the body mass index value: overweight group (body mass index > 25 kg/m², n=3), lean group (body mass index < 18 kg/m2, n=4), and normal group (body mass index 18-25 kg/m², n=13). A natural walking gait test was carried out on the three groups of subjects with a Zebris pressure distribution measurement plate to obtain the complete gait cycle parameters. The time proportion of support time phase, peak pressure, time to peak force, peak force and impulse volume were analyzed and the correlation between each parameter and the body mass index was analyzed by Person analysis. RESULTS AND CONCLUSION: (1) Compared with the other two groups, the time proportion of support time phase of subjects in the overweight group was relatively small, while the time proportion in the foot heel contact period and forefoot extension period was relatively large. There was a positive correlation of the time proportion of the foot heel contact period and forefoot extension period with body mass index, while there was a negative correlation between the time proportion of the arch support period and body mass index. (2) The peak pressure of the left arch and palm of the foot of the subjects of the overweight group was higher than that of the normal group, and the peak pressure of the left and right palm of the foot of the lean group was lower than that of the normal group. The peak pressure was positively correlated with the body mass index during the foot heel contact period. There was a significant positive correlation between the peak pressure of the left foot and body mass index during the arch support period as well as the peak pressure of both feet and body mass index during the forefoot extension period. (3) Plantar peak force time in the order of the gait cycle in increasing order: heel < arch < metatarsal < toe. In the foot heel contact period, the time of peak force was negatively correlated with body mass index, but they were positively correlated with each other in the forefoot extension period. In the arch support period, the time of peak force of the left arch was significantly positively correlated with body mass index. (4) Plantar peak force was mainly expressed as medial heel > toe/middle 2-4 metatarsal > lateral heel > medial and lateral metatarsal > arch; medial heel peak force was the largest, and the arch peak force was the smallest. Except for the toe of the left foot, there was a significant positive correlation between peak force and body mass index. (5) The maximum ground impulse of the lean group and the overweight group was in the foot heel contact stage, the minimum ground impulse was in the forefoot extension period, and the minimum ground impulse of the arch was in the normal group. There was a significant positive correlation between ground impulse and body mass index at different periods. (6) The results show that young people should control their body mass index, wear appropriate shoes, protect their feet and ankles, and prevent the occurrence of flat feet. [ABSTRACT FROM AUTHOR]

Eccentric quasi-isometric (EQI) contractions (maintaining a yielding contraction for as long as possible, beyond task failure) have gained interest in research and applied settings. However, little is known regarding the biomechanical profile of EQIs. Fourteen well-trained males performed four maximal effort knee-extensor EQIs, separated by 180 seconds. Angular impulse, velocity, and time-under-tension through the 30–100º range of motion (ROM), and in eight ROM brackets were quantified. Statistical parametric mapping, analyses of variance, and standardised effects (Hedges' g (ES), %Δ) detected between-contraction joint-angle-specific differences in time-normalised and absolute variables. Mean velocity was 1.34º·s−1 with most (62.5 ± 4.9%) of the angular impulse imparted between 40–70º. Most between-contraction changes occurred between 30–50º (p≤ 0.067, ES = 0.53 ± 0.31, 60 ± 52%), while measures remained constant between 50–100º (= 0.069–0.83, ES = 0.10 ± 0.26, 14.3 ± 24.6%). EQIs are a time-efficient means to impart high cumulative mechanical tension, especially at short to medium muscle lengths. However, angular impulse distribution shifts towards medium to long muscle lengths with repeat contractions. Practitioners may utilise EQIs to emphasize the initial portion of the ROM, and limit ROM, or apply EQIs in a fatigued state to emphasize longer muscle lengths. [ABSTRACT FROM AUTHOR]

In the protective engineering field, close-range explosions produce more energy and are more likely to cause severe damage to building structures than long-range explosions. In current standards, close-range explosions are defined as an explosion with a scale distance of less than 1.2 m/kg1/3. Besides, the steel plate's dynamic response is critical, especially under the blast loads generated by different shapes of explosives. For cylindrical explosives most commonly used in military and engineering, this study carried out experimental and numerical simulation studies on steel plates under the close-range air blast loads generated by different H/D cylindrical explosives (0.5≤H/D≤3.0). First, close-range air blast load tests were performed to study the failure modes of steel plates at different scale distances. The height-to-bottom diameter H/D ratio was defined as the shape factor of cylindrical explosive, and the effect of H/D on the failure deformation and dynamic response of the steel plate was quantitatively studied. Finally, the characteristics of shock waves generated by cylindrical explosives with different H/D were analyzed to determine the influence of H/D on the spatial distribution of shock waves. The results showed that with the increase of H/D , the steel plate deformation and damage gradually decreased. When the scale distance was more significant than or equal to 0.38, there was no crack in the steel plate, and the residual deflection gradually reduced with the increase of H/D. Despite the different scale distances, the residual deflections showed similar trends with increasing H/D. When the scale distance was less than or equal to 0.30, the steel plate cracked, and the crack area gradually decreased with increased H/D. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ordnance Equipment Engineering is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The objective of this study is to analyse the kinetic effects of acute fatigue during a 45° change of direction executed with the non-dominant limb, emulating a typical defensive action during pressing in soccer. Seventeen male professional soccer players (age: 21.7 ± 5.4 years) performed a 45° change of direction before and after a fatigue protocol. Participants were instructed to execute an approach run as quickly as possible, to change direction with their non-dominant foot on a force platform, and then continue running with the aim of stopping against an opponent. Times, forces, impulses, and force rates for different subphases during support were compared. Speeds remained consistent across pre-fatigue (4.53 ± 0.55 m s-1) and post-fatigue (4.58 ± 0.70 m s-1) trials. The results indicated a decrease in braking time (p = 0.01), impulse associated with the braking phase (p

To investigate the energetic release attributes and damage potential of a specific thermobaric explosive at atmospheric pressure, we had employed a pressure testing system, high-speed camera system, and thermal imager to elucidate the impact of explosive mass on the energetic release characteristics. Our findings underscored that thermobaric explosive can significantly enhance the after-burning effect. We noted a discernible positive relationship among the magnitude of the explosive force, post-detonation combustion effects, and the inherent quality of the given explosive. In addition, the resultant overpressure from the shockwave, positive pressure-area impulse, and the duration of the positive pressure, all markedly exceeded those produced by TNT, exhibiting increases of 38.9 %, 51.48 %, and 7 %, respectively. To quantify their explosive potency, empirical formulae were derived to account for the shock wave parameters of thermobaric explosive. Under equivalent mass conditions, the peak thermal radiation flux per unit area from thermobaric explosive substantially exceeded that of TNT. When the PROBIT (probability unit) model and the overpressure-impulse criteria were utilized to ascertain the damage potential of the respective explosives on human targets and structures, it emerged that TBX imparted superior destructive effects. This analysis underpinned the foundational assessment concerning the blast hazard presented by TBX.

Purpose: Evaluate the effects of 6 weeks of specific-joint isometric strength training on serve velocity (SV), serve accuracy (SA), and force–time curve variables. Methods: Sixteen young competition tennis players were divided into an intervention (n = 10) or control group (n = 6). SV, SA, maximal voluntary isometric contraction, peak rate of force development, rate of force development, and impulse (IMP) at different time frames while performing a shoulder internal rotation (SHIR) or flexion were tested at weeks 0, 3, and 6. Results: The intervention group showed significant increases in SV from pretest to posttest (7.0%, effect size [ES] = 0.87) and no variations in SA. Moreover, the intervention group showed significant increases from pretest to posttest in shoulder-flexion rate of force development at 150 (30.4%, ES = 2.44), 200 (36.5%, ES = 1.26), and 250 ms (43.7%, ES = 1.67) and in SHIR IMP at 150 (35.7%, ES = 1.18), 200 (33.4%, ES = 1.19), and 250 ms (35.6%, ES = 1.08). Furthermore, significant increases were found in shoulder-flexion rate of force development from intertest to posttest at 150 ms (24.5%, ES = 1.07) and in SHIR IMP at 150 (13.5%, ES = 0.90), 200 (19.1%, ES = 0.98), and 250 ms (27.2%, ES = 1.16). SHIR IMP changes from pretest to intertest were found at 150 ms (25.6%, ES = 1.04). The control group did not show changes in any of the tested variables. Conclusions: Six weeks of upper-limb specific-joint isometric strength training alongside habitual technical–tactical workouts results in significant increases in SV without SA detriment in young tennis players. [ABSTRACT FROM AUTHOR]

Context: Intrasession reliabilities of isometric knee extension kinetics via portable strain gauge have been reported across several knee joint angles and constraints. However, intersession variabilities, which are more valuable, have yet to be determined. Therefore, we aimed to quantify the intersession variability of knee extension kinetics over 3 testing sessions using an affordable and portable strain gauge. Design: Participants performed maximum voluntary isometric contractions of the knee extensors over 3 sessions. Methods: Eleven (6 men and 5 women; 31 [6.4] y) volunteers performed maximum voluntary isometric contractions in constrained (isokinetic setup with thigh and chest straps) and unconstrained (treatment plinth) conditions. Peak force (PF), peak rate of force development, rate of force development (RFD), and impulse (IMP) from 20% to 80% of PF were assessed. Means, SDs, percentage changes, minimal detectable changes, coefficients of variation (CV), and intraclass correlation coefficients (ICC) were calculated and reported. Results: PF had the lowest intersession variability regardless of condition (CV = 5.5%–13.8%, ICC =.67–.93). However, variability of peak rate of force development (CV [range] = 12.2%–24.7%, ICC =.50–.78), RFD (CV = 10.0%–26.8%, ICC =.48–.84), and IMP (CV = 15.2%–35.4%, ICC =.44–.88) was moderate at best. The constrained condition (CV [SD] = 14.1% [4.8%], ICC =.74 [.08]) had lower variability compared with the plinth (CV = 19.8% [7.9%], ICC =.68 [.15]). Variability improved from sessions 1 to 2 (CV = 20.4% [7.7%], ICC =.64 [.14]) and to sessions 2 to 3 (CV = 15.3% [6.4%], ICC =.76 [.10]). Conclusions: PF can be assessed regardless of setup. However, RFD and IMP changes across sessions should be approached with caution. Backrests and thigh straps improve RFD and IMP variability, and at least 1 familiarization session should be provided before relying on knee-extensor kinetics while utilizing a portable strain gauge. [ABSTRACT FROM AUTHOR]

In this work, we investigate a Riemann-Liouville-type impulsive fractional integral boundary value problem. Using the fixed point index, we obtain two existence theorems on positive solutions under some conditions concerning the spectral radius of the relevant linear operator. Our method improves and generalizes some results in the literature.

The study aimed to identify and explain the typical differences in low-intensity high-volume resistance training (LIHV-RT) performances for major muscle groups between rural versus urban young female students to establish the relevant set of quantitative and qualitative resistance training parameters. The study sample included 46 recreational active female students at the Transilvania University of Brasov, (mean ± SD age, 20 ± 1year; body mass, 60 ± 3 kg; height, 160 ± 4 cm) grouped urban vs. rural. The study used modified resistance exercise machines for the hamstring- and quadricep-group muscles, equipped with a dynamometer and sensors for identifying developed forces and accelerations. A number of 368 tests were performed, representing two attempts for each subject, for knee flexion and knee extension exercises, with two different loads. For the performance analysis some variables were considered: the maximum number of repetition until failure, maximum force developed, maximum acceleration, the duration of the set and the mean time per repetition. The maximum number of repetition to failure shows a significant higher value for rural than urban in case of knee flexion (d = 0.98 [0.32, 1.54] for load 1(L1) and d = 0.65 [0.03, 1.21] for load 2(L2)) and in case of knee extension (d = 1.89 [1.11, 2.48] for L1 and d = 1.67 [0.92, 2.25] for L2). The total duration of the sets shows a significant higher value for rural than urban in case of knee flexion (d = 0.84 [0.19,1.39] for L2) and in case of knee extension (d = 1.46 [0.74, 2.03] for L1 and d = 1.56 [0.98, 2.14] for L2). Additionally we found differences in the quality of the relevant repetitions execution and in the impulse developed during the LIHV- MNRF sets. The study's main finding was that there are differences in LIHV- RT performances knee flexion and knee extension antagonistic exercises, between rural and urban female students. We concluded that the obtained results allow teachers to understand the optimal design of RT programs for the different groups of participants, in order to adapt their teaching techniques so that their final objectives are achieved, insisting on particular aspects of the theoretical or practical contents. [ABSTRACT FROM AUTHOR]

Background Isokinetic dynamometers are widely used when assessing neuromuscular function including knee extension kinetics. However, these dynamometers are often prohibitively expensive and are not portable. Thus strain-gauge technology has grown in popularity. Purpose The purpose of this study was to compare kinetic data captured via an isokinetic dynamometer against an affordable and portable strain-gauge with a treatment plinth during maximal isometric knee extensions. Study Design Cross-sectional study. Methods Healthy participants (8 males and 6 females; age 30.2±7.1 years) volunteered and performed knee extensions at a 90° knee angle on a dynamometer and a treatment plinth with a portable strain-gauge. Peak force (PF), peak rate of force development (PRFD), rate of force development (RFD2080) and impulse (IMP2080) from 20-80% of onset to peak force were assessed using both strain-gauge and isokinetic dynamometer. Between-device differences were evaluated by the Wilcoxon signed-rank test, Cohen's d effect sizes (ES), Pearson's correlation coefficients (r), and Bland-Altman plots. Results No significant or meaningful differences were identified between isokinetic and strain-gauge devices (all p≥0.268, ES≤0.35). However, slightly greater (2.5-9.5%) outputs were observed with the isokinetic dynamometer. Very large significant between-device correlations were found for PF (r=0.77, p=0.001) and PRFD (r=0.73, p=0.003), while small and moderate non-significant between-device correlations were found for RFD2080 (r=0.48, p=0.079) and IMP2080 (r=0.59, p=0.060). Bland-Altman plots did not reveal apparent biases from high to low performers. Conclusions These results indicate that the strain-gauge device can produce valid maximal and rapid force expression measurements. Similar results, such as those quantified via an isokinetic device, can be obtained without extreme rigour and constraint. The study's findings support using the practically relevant treatment plinth and strain-gauge combination as a suitable alternative to the isokinetic dynamometry for measuring PF and PRFD. Therefore, more rehabilitation and sports performance practitioners can confidently assess knee extension kinetics. Level of Evidence 3 [ABSTRACT FROM AUTHOR]

Previous research addressed the spatiotemporal variables of the drop jump (DJ) versus the horizontal drop jump (HDJ). This study compared the kinetic variables of the DJ versus the HDJ in elite jumpers and sprinters. In a single session, sixteen elite jumpers and sprinters performed two DJ attempts with three different fall heights (0.30 m, 0.40 m, and 0.50 m), and after 2 h, performed two HDJ attempts from the same fall heights (0.30 m, 0.40 m, and 0.50 m). Kinetic variables: eccentric ground reaction forces (GRFE) and concentric ground reaction forces; eccentric impulse (PE) and concentric impulse (PC); peak power in the concentric phase; and rate of force decrease (RFDe) were measured using a research-grade force plate. The Wilcoxon test was used to compare the vertical and anteroposterior axes. GRFE was significantly higher (p ≤ 0.05) in the DJ vs the HDJ with large effect sizes. The PE (p ≤ 0.006) and PC (p = 0.002) were significantly lower in the DJ than in the HDJ. The RFDe was also significantly lower in the DJ at 0.30 m vs. the HDJ at 0.30 m (p = 0.002). In summary, elite jumpers and sprinters may benefit from incorporating both the DJ and the HDJ into their training regimens, with the DJ being particularly advantageous for enhancing power metrics and RFDe. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ordnance Equipment Engineering is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, stability analysis and stabilization control of discrete-time impulsive switched time-delay systems with all unstable subsystems are discussed. By utilizing a switching time-varying Lyapunov-Krasovskii functional and the mode-dependent interval dwell-time switching rule, we derive some more general stability theorems for the considered time-delay system with all subsystems being unstable. Moreover, we design a time-varying state feedback controller to ensure the stabilization of the resulting closed-loop system. Eventually, the theoretical findings are demonstrated utilizing numerical examples. [ABSTRACT FROM AUTHOR]

RDX/HMX-TNT-based aluminized explosive compositions have been investigated to find empirical relations based on heat of explosion (Q) and velocity of detonation (VOD) for calculation of peak over pressure (POP) and impulse (I). Four HMX-TNT-based aluminized compositions have been selected based on calculated values of Q and explosive power. Explosive charges of RDX/HMX-TNT-based aluminized compositions and TNT have been prepared by melt-cast technique for measurement of VOD and air blast. Cylindrical explosive charges with length to diameter ratio of ~ 1 and weight ~ 1.3 kg have been used for measurement of pressure-time profiles at standoff distance of 2–6 m. Similar measurements were also performed for the explosive charges of TNT of weight ~ 11 and 17 kg. Normalized values of Q and VOD2 with corresponding values of TNT have been used to compute charge weight for calculation of scaled distance which is termed as normalized scaled distance. Form of empirical relations has been decided from variation of POP and I with normalized scaled distance. Values of constants used in these relations have been determined using regression analysis. Validation of empirical relations has been carried out by comparing calculated and experimental values of POP and I for explosive charges. [ABSTRACT FROM AUTHOR]

The asymptotic synchronization of quaternion-valued delayed neural networks with impulses and inertia is studied in this article. Firstly, a convergence result on piecewise differentiable functions is developed, which is a generalization of the Barbalat lemma and provides a powerful tool for the convergence analysis of discontinuous systems. To achieve synchronization, a constant gain-based control scheme and an adaptive gain-based control strategy are directly proposed for response quaternion-valued models. In the convergence analysis, a direct analysis method is developed to discuss the synchronization without using the separation technique or reduced-order transformation. In particular, some Lyapunov functionals, composed of the state variables and their derivatives, are directly constructed and some synchronization criteria represented by matrix inequalities are obtained based on quaternion theory. Some numerical results are shown to further confirm the theoretical analysis. [ABSTRACT FROM AUTHOR]

We introduce and study a new class of nonlinear multi-term impulsive fractional q-difference equations supplemented with nonlocal boundary conditions. The classical fixed point theorems are applied to show the existence and uniqueness of solutions to the given problem. Examples are presented for illustrating the abstract results. Several new results appear as special cases of the ones presented in this article. [ABSTRACT FROM AUTHOR]

The primary aim of this study was to investigate the stability of the six-repetition maximum (6RM) deadlift over the length of a five-day microcycle and whether the fatigue induced by maximal effort testing detrimentally impacted preparedness. Twelve participants performed four testing sessions, comprising a one-repetition maximum test and three 6RM tests separated by 48 hours. Countermovement jumps were performed before each testing session, and barbell velocity was measured during each warm-up set to assess changes in preparedness. The 6RM deadlift was not statistically different between any of the testing sessions (p =.056; ηp2 = 0.251). Similarly, there were no significant differences in jump height or other CMJ variables between sessions (p >.05). There were small to moderate differences in mean barbell velocity between the first and second 6RM test (g = 0.24–0.88), while there were only small differences in mean velocity (MV) between the second and third 6RM test at some of the warm-up loads (40% 6RM: g = 0.20; 80% 6RM: g = −0.47). Taken collectively, these data indicate that 6RM deadlift strength is stable over five days and does not appear to induce sufficient fatigue to impact vertical jump performance or rating of perceived exertion despite some changes in barbell velocity. [ABSTRACT FROM AUTHOR]

The guaranteed cost finite-time stability of positive switched fractional-order systems (PSFS) with D-disturbance and impulse is studied based on the Φ -dependent average dwell time (Φ DADT) strategy. Firstly, the finite-time stability of the studied system is proved by constructing a linear co-positive Lyapunov function. Secondly, the system's guaranteed cost analysis is given with the estimated upper bound of the cost. In addition, the finite-time certain and robust controllers are designed to ensure the system's stabilization. A numerical example is finally given to signify the validity of the conclusions. [ABSTRACT FROM AUTHOR]

Copyright of Cultura, Ciencia y Deporte is the property of Cultura, Ciencia y Deporte and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)